1. Field of the Invention
The present invention relates to a new gene encoding a glycine-rich polypeptide, and an expression vector, host cell and transgenic plant comprising the gene.
2. Description of the Prior Art
Plants have evolved many mechanisms against pathogen attack such as hypersensitive response (HR), systemic acquired resistance (SAR), and induced systemic resistance (ISR). SAR is evolved to defend pathogens in wide spectrum that is associated with sophisticated physiological and biochemical changes in plants (Ryals et al., 1996, Plant Cell 8: 1809-1819). SAR can be induced either by phytopathogens or chemicals (Kessmann et al., 1994, Annu. Rev. Phytopathol. 32: 439-459). In the pathogen-induced SAR, pathogens such as viruses, bacteria and fungi cause a cell death response and activate SAR in plants. As to the chemical-induced SAR, salicylic acid and probenazole are two representative chemicals for inducing SAR. For example, salicylic acid (SA), which is a well-known SAR inducer, plays an important role in the induction of plant defense. The researches with nahG transgenic plants suggest that SA is required for the development of SAR and has been reported to act as a secondary signal to elicit plant defense responses, as described in Metraux, 2001, Eur. J. Plant Pathol. 107: 13-18. Midoh and Iwata indicated that the probenazole induced the expression of defense-related genes (Midoh and Iwata, 1997, J. Pesticide Sci. 22: 45-47). Yoshioka et al. described that probenazole induced systemic acquired resistance in Arabidopsis with a novel type of action (Yoshioka et al., 2001, Plant J. 25: 149-157).
The accumulation of a group of proteins called pathogenesis-related proteins (PR proteins) correlates with the onset of SAR. The induction of PR proteins is considered to be the components of biochemical defenses. The PR proteins include PR1, β-1,3-glucanase, chitinases, lysozymes, PR4, thaumatin-like proteins, osmotin-like proteins, cysteine-rich proteins, glycine-rich proteins, proteinase inhibitors, proteinases, peroxidases, etc., which can build up the capability of disease resistance in plants to defend pathogen attack (Agrios G. N., 1997, Plant pathology, Academic press, San Diego, USA; Linthorst, 1991, Critical Rev. Plant Sci. 10:123-150). The expression of many defense-related genes during elicitation of SAR have been demonstrated. It is suggested that the genes are involved in both of biochemical and structural defenses of plants. It is believed that SAR-induced genes can enhance a plant's resistance to fungal attack.